Clearing autocomplete entries from Apple Mail

As part of my new year cleanup of all things tech in my house, my laptop is getting some much needed sprucing up. I've made a concerted effort to decrease the amount of clutter in my Mail app. Previously I was using two email accounts and I've decided that this is not very efficient.

In the midst of doing this, I've noticed a lot of old auto-complete entries for people I've exchanged digital correspondence with a time or two. Add in the fact that my OCD likes to work on overtime, you can imagine this was a sore spot for me for a very long time. I've done a post on this in the past. I thought it might be good to mention it again, in the spirit of the new year and cleaning out old data from your applications.

If anyone has an idea on where stores auto complete data, I'd be very interested in doing a post on this. I've looked all over - in the container, in the application preferences folder - and have found nothing so far.